Method for reducing the noise in a wobble signal

ABSTRACT

The present invention relates to a method and a circuit for recovering information contained in a wobble track of an optical storage medium. One aim of the invention is to describe a method within an appliance for reading from and/or writing to optical storage media, which can correct disturbing data signal components in the wobble signal even when the swept frequency and the lowest signal frequency are close to one another. According to the invention, this object is achieved in that the signals from two detector halves of a photodetector which is used for reading the data contained in a track on an optical storage medium are provided with weighting factors which are adjusted dynamically during operation of the appliance for reading from and/or writing to optical storage media. In order to adjust the weighting factors, the obtained swept-frequency signal is linked to a data signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit, under 35 U.S.C. § 365 ofInternational Application PCT/EP02/08706, filed Aug. 5, 2002, which waspublished in accordance with PCT Article 21(2) on Feb. 27, 2003 inEnglish and which claims the benefit of German patent application No.10140325.9, filed Aug. 16, 2001.

The present invention relates to a method and a circuit for recoveringthe information contained in a wobble track of an optical storagemedium.

FIELD OF THE INVENTION

Methods such as these are used, for example, in appliances for readingfrom and/or writing to optical storage media with wobble tracks, inorder to obtain address information from the wobble tracks or to use thewobble frequency to produce a write clock.

BACKGROUND OF THE INVENTION

In general, in optical storage media which are in the form of discs andare suitable for reading from and/or writing the embossed tracks areformed such that they represent an interleaved spiral or concentriccircles. Especially in the case of optical storage media which aresuitable for writing to, the embossed tracks additionally are wobbled ina specific form, in order to find specific positions on the medium. Thismeans that the track is not embossed in an approximately straight line,but in serpentine lines. By way of example, the shape of theseserpentine lines can contain address information which is used toidentify a specific position on this optical storage medium. Variousmethods are used for coding, examples of which include frequencymodulation or phase modulation. Furthermore, the wobble signal may alsobe used for rotation speed information or for presetting a write datarate.

Normally, the modulation shift of this track wobble is kept small, sothat there is no noticeable effect on the tracking control and the readquality of the data signal. The modulation shift is thus kept in theorder of magnitude of a few percent of the track separation.Furthermore, the modulation frequency is designed to be in a frequencyband which is typically above the upper cut-off frequency of thetracking regulator, but is below the lowermost signal frequency of thedata signal. However, the small modulation shift means that thesignal-to-noise ratio of the wobble signal obtained from it isrelatively low. Nevertheless, the coded information and the fundamentalfrequency should be capable of being coded and reconstructed reliably,in order to allow reliable reading and writing. Disturbance noisecomponents must therefore be effectively suppressed.

U.S. Pat. No. 5,717,679 discloses a system which is able to correct thenoise components in the wobble signal resulting from any eccentricity ofthe wobble track. The circuit which is specified for this purpose usesvariable-gain amplifiers in order to compensate for differentillumination levels of two detector halves. The system is based on theCD-R technique, which uses a wobble frequency of 22.05 kHz. Since thelowest signal frequency of the data signal is 934 kHz, those data signalcomponents which are likewise present in the wobble signal can easily beremoved by means of a low-pass filter, as is also disclosed in U.S. Pat.No. 5,717,679. One disadvantage of this known system is that low-passfiltering is impossible when using wobble frequencies which are close tothe lowest signal frequency, as is the case, for example, with DVDtechnology (wobble frequency 825 kHz). Disturbance data signalcomponents therefore cannot be removed with the disclosed system at highwobble frequencies.

One aim of the invention is to describe a method within an appliance forreading from and/or writing to optical storage media, which can removedisturbance data signal components in the wobble signal even when thewobble frequency and the lowest signal frequency are close to oneanother.

According to the invention, this object is achieved in that the signalsfrom two detector halves of a photodetector from which a wobble signalis obtained and which is used for reading the data contained in a trackof an optical storage medium are provided with weighting factors whichare adjusted dynamically during operation of the appliance. In order toadjust the weighting factors, the data signal component in the wobblesignal that is obtained is linked to the data signal. Dynamic adjustmentof the weighting factors has the advantage that the data signalcomponents in the wobble signal are always suppressed optimally, even ifany changes occur in the illumination level of the photodetector duringoperation.

SUMMARY OF THE INVENTION

According to the invention, the signals from the two detector areas ofthe photodetector are provided with mutually opposing weighting factors.This has the advantage that the amplitude of the wobble signal obtainedfrom the difference between the signals from the two detector areas isnot influenced by the weighting factors.

According to the invention, the data signal is digitized before beinglinked to the data signal component of the wobble signal, so that thelinking process is carried out as a synchronous demodulation process.The advantage of using a digitized data signal is that the synchronousdemodulation represents multiplication by ±1, and, technically, this canbe carried out easily.

The wobble signal is advantageously normalized before determining thedata signal component. This may be done, for example, by means of anaveraged sum signal or the signal from one detector half. Inconsequence, the amplitude of the wobble signal is less dependent on thelight power of a light source in the optical scanner, or reflection onthe optical storage medium. The reaction time of the control loop todynamic adjustment of the weighting factors is then likewise lessdependent on these variables. One advantage of using an averaged sumsignal is that such an averaged sum signal is generally alreadyavailable in appliances for reading from and/or writing to opticalstorage media.

In a further method according to the invention, the amplitude of thewobble signal is kept constant, by the signals from the two detectorhalves being normalized separately by means of their respective averagedsum signal.

According to the invention, disturbance data signal components in thewobble signal are removed by means of a circuit which uses one of themethods mentioned above.

A method according to the invention or a circuit according to theinvention is advantageously used for recovering the informationcontained in a wobble track in an optical storage medium in an appliancefor reading from and/or writing to optical storage media.

BRIEF DESCRIPTION OF THE FIGS.

The invention will be explained in the following text with reference toadvantageous exemplary embodiments and using FIGS. 1 to 9. Combinationsof advantageous exemplary embodiments are, of course, within theapplicability area of the invention. In the figures, identical referencesymbols denote the same components and signals. In the figures:

FIG. 1: shows an arrangement for obtaining a wobble signal according tothe prior art;

FIG. 2: shows an arrangement according to the invention for automaticadjustment of the weighting factors;

FIG. 3: shows a modification of the arrangement corresponding to FIG. 2;

FIG. 4: shows an arrangement corresponding to FIG. 2 with amplituderegulation of the data signal;

FIG. 5 shows an arrangement corresponding to FIG. 2 with the data signalbeing normalized;

FIG. 6: shows an arrangement corresponding to FIG. 2, with the wobblesignal being normalized;

FIG. 7: shows an arrangement corresponding to FIG. 2 with amplituderegulation of the wobble signal;

FIG. 8: shows an arrangement corresponding to FIG. 2, with the signalsof the two detector halves being normalized; and

FIG. 9: shows an appliance for reading from and/or writing to opticalstorage media, which has an arrangement according to the invention forautomatic adjustment of the weighting factors.

DETAILED DESCRIPTION

FIG. 9 shows an appliance for reading from and/or writing to opticalstorage media 34, which has an arrangement 38 according to the inventionfor obtaining information INF contained in a wobble track 36 on theoptical storage medium. The scanning beam 40 which is emitted from alight source 30 is collimated by a collimator 31, and is diverted bymeans of a beam splitter 32. An objective lens 33 focuses the scanningbeam 40 onto the wobble track 36 of a layer 35 of an optical storagemedium 34 which carries information. The scanning beam 40 reflected fromthe layer which carries the information is collimated by the objectivelens 33 and is imaged on the photodetector 1 by means of an imaging unit37. A tracking error signal TW′ and the information INF are obtainedfrom the signals A, B, C, D from the photodetector 1 by means of anarrangement 38 according to the invention for recovering the informationINF contained in a wobble track 36 of an optical storage medium 34. Thetracking error signal TW′ is supplied to a tracking regulator 39, whichitself ensures that the scanning beam 40 moves as close as possible tothe track centre of the wobble track 36.

FIG. 1 shows an arrangement for obtaining a wobble signal TW, which isused by a decoding unit 8 to decode the information INF contained in thewobble track 36 of an optical storage medium 34, according to the priorart. The basis for obtaining the signal is the linking of the signals A,B, C, D from a photodetector 1. This makes use of the characteristicthat the scanning beam 40 which strikes the optical storage medium 34 asshown in FIG. 9 causes an effect which makes it possible to use thepush-pull tracking control method. This effect is based on the principlethat a diffraction effect occurs at the edges of the tracks 36, so thatnot only is a vertical beam (zeroth order) reflected in the direction ofthe photodetector 1 from the memory layer 35 which carries theinformation, but also higher-order beams, which are not reflectedprecisely at right angles to the surface of the memory layer 35. In thiscase, an objective lens 33 is generally used to collect the reflectedzeroth order and ±1^(st) order beams and to image them on aphotodetector 1, which is subdivided into at least two areas 1A+1D,1B+1C. In the process, destructive interference of different intensityis formed in the overlapping area between the zeroth order and ±1^(st)order as a function of the tracking position, and this is evaluated inthe form of a tracking error signal TW′. The resultant tracking errorsignal TW′is thus referred to as the push-pull tracking error signal.

In order to obtain this tracking error signal TW′, the output signals A,B, C, D from the photodetector 1 are first of all amplified by means ofamplifiers 2, and are then linked, for example as shown in FIG. 1. Thephotodetector 1 is typically subdivided into four areas 1A, 1B, 1C, 1D,in order to obtain a focusing error signal (not shown) at the same time,in addition to the tracking error signal TW′. However, in order toobtain the tracking error signal TW′ using the push-pull effect, it issufficient to subdivide the photodetector 1 into a right-hand half 1B+1Cand a left-hand half 1A+1D, and to subtract the output signals fromthese two detector halves from one another. In the case of afour-quadrant detector, this is done by first of all carrying out thelogic operations (A+D) and (B+C) using two adders 4, 5. The differencesignal (A+D)−(B+C) is then formed by means of a differential amplifier6. The difference signal (A+D)−(B+C) obtained in this way is thensupplied to a tracking regulator 39, as the tracking error signal TW′.The tracking regulator 39 for its part ensures that the scanning beam 40is moved as close as possible to the track centre of a predeterminedtrack 36.

In order to decode the information INF contained in the wobble tracks 36of an optical storage medium 34, or in order to form a write clock, thewobble signal TW is supplied to a decoding unit 8 which, by way ofexample, emits address information and/or a write clock. The wobblesignal TW is itself formed by filtering from the push-pull trackingerror signal TW′, by means of a filter 7.

On the other hand, the data signal HF which represents the informationcontent of the optical storage medium 34 is formed from the outputsignals A, B, C, D from the photodetector 1 by addition in an adder 3.In order to allow detection by addition of the photodetector signals A,B, C, D, the information is stored by writing light/dark contrasts or byembossing so-called pits on the optical storage medium 34.

If the scanning beam 40 is following the centre of an embossed track 36,the scanning beam 40 is reflected at the layer 35 of the optical storagemedium 34 which carries the information, such that, ideally, a roundlight spot is imaged onto the photodetector 1, at whose sides thealready mentioned interference resulting from the push-pull effect isobserved. The total intensity of this light spot is modulated by thebrightness contrast of the area illuminated by the scanning beam 40.

Since the data is stored by means of structures which cause brightnessdifferences, the intensity of the light spot is thus modulated such thatit corresponds to the data on the memory layer 35. Ideally, this iscarried out in a synchronized manner on the two detector halves 1A+1D,1B+1C. Since the tracking error signal TW′ and the wobble signal TWderived from it are derived from the difference (A+D)−(B+C) between thesignals from the detector halves 1A+1D, 1B+1C the data signal componentcaused by the brightness contrast is cancelled out during thesubtraction process by the differential amplifier 6. However, if theimaging of the scanning beam 40 on the photodetector 1 is not ideallyaxially symmetrical, then a data signal component AS′ is superimposed onthe desired signal component which represents the wobble track 36. Thisresults in it not being possible to evaluate those signal componentswhich are caused by the wobble track 36 as well as before, so thaterrors occur in the address evaluation.

An improvement is achieved if the weighting between the output signals(A+D), (B+C) from the two halves 1A+1D, 1B+1C of the photodetector 1 ischanged before the subtraction process by the differential amplifier 6,so that the contrast-dependent components of the alternating lightamplitudes are cancelled out on the two halves 1A+1D, 1B+1C of thephotodetector 1.

To this end, the four photodetector signals A, B, C, D are first of allamplified by means of amplifiers 2. Two signal elements (A+D), (B+C) arethen produced by summation in the adders 4, 5 and these reproduce themodulation on the respective halves 1A+1D, 1B+1C of the photodetector 1.Before the subsequent subtraction process, the signal (A+D) is passedthrough an amplifier 9K1 with a variably adjustable gain K1, so that thedifference signal TW′ is formed in accordance with the followingrelationship:TW′=K 1×( A+D)−(B+C)

The weighting process results in the data signal components which areimaged onto the detector halves 1A+1D, 1B+1C as a result of thedifferent modulation being set to the same magnitude before thesubtraction process, so that they cancel one another out. This can alsobe achieved in an equivalent manner by passing the signal (B+C) throughan amplifier 9K2 with a variably adjustable gain K2, corresponding tothe following signal calculation:TW′=(A+D)−K2×(B+C)

The two solutions have the common feature that the resultant amplitudeof the difference signal TW′ changes as a function of the weightingfactor K1, K2 setting. This can be avoided by the two signals (A+D),(B+C) being weighted, and by the weighting factors K1, K2 being matchedto one another such that K2=1−K1. The following signal calculation isthus used:TW′=K1×(A+D)−(1−K1)×(B+C)

The tracking error signal TW′ normally has any further undesirablesignal components, such as low-frequency disturbances caused by residualtracking errors and so on, removed from it by means of a filter 7, inorder to obtain the wobble signal TW which is supplied to the decodingunit 8.

During operation of the appliance for reading from and/or writing tooptical storage media 34, it is possible, however, for a situation tooccur caused by heating, ageing or other disturbance variables in whichthe intensity distribution or position of the image on the photodetector1 changes. A situation such as this can occur in particular as a resultof residual errors in focus control or in tracking control 39. If theweighting factors K1, K2 are set only once during production of theappliance, it is impossible to compensate for such variables, which varydynamically.

In order to overcome this disadvantage, it is advantageous to adjust theweighting factors K1, K2 automatically during operation such that thedisturbance data signal components cancel one another out as well aspossible in the subtraction process 6.

An arrangement according to the invention for automatic adjustment ofthe weighting factors K1, K2, in which the data signal HF obtained bysummation of the signals A, B, C, D from the photodetector 1 ismultiplied by the data signal component AS′ from the difference signalTW′ or from the wobble signal TW, the result of the multiplication isintegrated, and the result of the integration used to adjust theweighting factors, is shown in FIG. 2.

The difference signal TW′ obtained in the manner described in FIG. 1 haslow-frequency disturbances removed from it by means of a filter 10 whichcan pass only the data signal frequency band, and this is supplied to afirst input of a multiplier 11. The wobble signal TW can also be usedinstead of the difference signal TW′. The second input of the multiplier11 is supplied with the data signal HF which also has low-frequencydisturbances removed from it by means of a filter 10 b. The outputsignal from the multiplier 11 is integrated by an integrator 12. Theoutput signal from the integrator 12 controls the first weighting factorK1, while the output signal converted by a converter 13 controls thesecond weighting factor K2. The converter 13 is, for example, a divider,an inverter or a functional block which calculates the value 1−x to avalue x. Other converters may of course also be used.

The invention is based on the alternating light modulations on the twodetector halves 1A+1D, 1B+1C being in phase with one another. For thisreason, the sum of the output signals A, B, C, D from the photodetectorareas 1A, 1B, 1C, 1D is used to obtain the data signal. The voltageproduced in the photodetector 1 is in this case proportional to theintensity reflected from the optical storage medium 34.

A corresponding situation applies to the two detector halves 1A+1D,1B+1C, so that if the weighting K1, K2 is set to be the same in the twobranches during the subtraction process by means of the differentialamplifier 6, the data signal components cancel one another out, providedthe amplitudes are equal. However, if there is an amplitude difference,then an undesirable data signal component AS′ remains in the differencesignal TW′ after the subtraction process, and this is also present inthe wobble signal TW after filtering by the filter 7. This data signalcomponent AS′ is at a phase angle of 0° or 180° relative to the datasignal HF, depending on which half 1A+1D, 1B+1C of the photodetector 1receives more reflected light. In the example shown in FIG. 2, the phaseangle between the data signal HF and the data signal component AS′ inthe difference signal TW′ will be zero when the detector half 1A+1D isilluminated more strongly. When the detector half 1B+1C is illuminatedmore strongly, then the negative mathematical sign in the subtractionprocess for the difference signal TW′ means that the phase angle betweenthe data signal HF and the data signal component AS′ in the differencesignal TW′ will be 180°. At the limit, when the modulations on thedetector halves 1A+1D, 1B+1C are equal or the weighting, K1, K2 is setcorrectly, the data signal component AS′ in the difference signal TW′ iszero, and thus in the ideal case, no phase angle can be found.

This behaviour is made use of by multiplying the data signal HF by thedata signal component AS′ in the difference signal TW′. Thismultiplication results in an output signal whose mathematical sign ispositive or negative depending on the phase angle, and whose magnitudeis dependent on the amplitude of the data signal component AS′ in thedifference signal TW′. The magnitude of the output signal from themultiplier 11 becomes greater the greater the difference between thedata signal components in (A+D) with reference to (B+C). Themathematical sign indicates which of the signal components is larger andshould be attenuated by appropriate weighting K1, K2.

If the output from the multiplier 11 is connected to an integrator 12,then the integrator 12 changes its output voltage until the data signalcomponent AS′ in the difference signal TW′ becomes zero. If the outputsignal from the integrator 12 sets the weighting factor K1, K2 of theone or the two branches to form the difference signal TW′, then thisresults in a control loop with an integrating response. In this case,the integrator 12 varies the weighting K1, K2 until the output signalfrom the multiplier 11 becomes zero.

The data signal component AS′ in the wobble signal TW is thus likewisezero. Since only the data signal components AS′ are intended to bemultiplied by one another, it is advantageous, as shown in FIG. 2, toremove the low-frequency components from the input signals to themultiplier 11. This can be done, for example, by means of high-pass orbandpass filters 10 a, 10 b, which allow only the data signal frequencyband to pass. For reasons of clarity, these filters 10 a, 10 b are notshown in the other figures.

The advantage of an integrating control loop response is that, after atime which is dependent on the integration time constant, the weightingK1, K2 is always set such that the data signal component AS′ in thewobble signal TW becomes zero. The remaining residual error, that is tosay in this case the data signal component AS′ in the wobble signal TW,will always become zero when the control loop has an integratingresponse. However, the integration time is dependent on the magnitude ofthe signal at the input of the integrator 12, that is to say in the caseof the weighting factor control loop, from the amplitude of the outputof the multiplier 11. This amplitude is in turn dependent on theamplitude of the input signals to the multiplier 11, that is to say fromthe data signal HF and the data signal component AS′ in the wobblesignal TW. If, for example, the light power from the light source 30 inthe optical scanner or the reflection of the optical storage medium 34is halved, then the output amplitude of the multiplier 11 is divided byfour, which means that the integration time is increased by a factor of4.

FIG. 3 shows an arrangement corresponding to that in FIG. 2, in which asynchronous demodulator 14, which has a digital input and an analogueinput, is used instead of the multiplier 11. The data signal componentAS′ of the difference signal TW′ is supplied to the analogue input ofthe synchronous demodulator 14. The data signal HF is digitized by meansof a comparator 15, and the digitized data signal HFD is then suppliedto the digital input of the synchronous demodulator 14. The weightingfactors K1, K2 are set as already described with reference to FIG. 2.Firstly, this arrangement has the advantage that the amplitude of thedigitized data signal HFD can assume only two fixed values, as a resultof which the integration time is less dependent on the light power fromthe light source 30 in the optical scanner or the reflection of theoptical storage medium 34. On the other hand, the multiplication by thedigitized data signal HFD represents a multiplication by ±1, which istechnically simple to implement.

FIG. 4 shows a further exemplary embodiment according to the invention,corresponding to that shown in FIG. 2, in which the amplitude of thedata signal HF is kept constant by an amplitude regulator 16. Ananalogue multiplier 11 is used in this case.

FIG. 5 shows an arrangement corresponding to that in FIG. 2, in whichthe amplitude of the data signal HF is normalized with the aid of theaveraged sum signal UMIA. For this purpose, the data signal HF issupplied to an averager 18, whose output signal UMIA is applied to anormalizer 17, and is used to normalize the data signal HF. An analoguemultiplier 11 is used in this case as well.

Both exemplary embodiments have the advantage that the amplitude of thedata signal HF is kept constant, so that the integration time is lessdependent on the light power from the light source 30 in the opticalscanner or the reflection of the optical storage medium 34. Furthermore,a normalized data signal is generally available in appliances forreading from and/or writing to optical storage media, so that theavailable signal can advantageously be used.

The arrangement shown in FIG. 6 differs from the arrangement shown inFIG. 5 in that the difference signal TW′ is normalized, instead of thedata signal HF, by the averaged sum signal UMIA. The output signal UMIAfrom the averager 18 is supplied to a normalizer 19, which normalizesthe difference signal TW′ on the basis of the signal UMIA.

The arrangement shown in FIG. 7 corresponds to the arrangement in FIG. 4with the difference that the amplitude of the difference signal TW′,rather than the amplitude of the data signal HF, is kept constant by anamplitude regulator 20.

The advantage of the two arrangements mentioned above is that theintegration time is less dependant on the light power from the lightsource 30 in the optical scanner, or the reflection of the opticalstorage medium 34.

The signals (A+D), (B+C) from the two detector halves 1A+1D, 1B+1C areadvantageously normalized separately, by means of their respectiveaveraged sum signal, before amplification by the variable amplifiers9K1, 9K2 and before subtraction by the differential amplifier 6, as isillustrated in FIG. 8. The sum signal (A+D) from the first detector half1A+1D is for this purpose supplied to the averager 21, whose outputsignal is supplied to the normalizer 22 and is used to normalize the sumsignal (A+D). In a corresponding way, the sum signal (B+C) from thesecond detector half 1B+1C is normalized by means of the averager 23 andthe normalizer 24.

The advantage of this arrangement is that the amplitudes of the signals(A+D), (B+C) from the two detector halves 1A+1D, 1B+1C are completelyindependent of the reflection and of the light power.

One of the arrangements shown in FIG. 2 to FIG. 8 is advantageously usedin an appliance for reading from and/or writing to optical storage mediawith wobble tracks as is shown in FIG. 9.

1. A method for obtaining information from a wobble track of an optical storage medium by producing a wobble signal from the difference between the signals from two photodetector areas of a photodetector, with the signal from one detector area being provided with a weighting factor, wherein a data signal, which is obtained by summing the signals from the photodetector, is linked to a data signal component which is contained in the wobble signal and is used for automatic adjustment of the weighting factor.
 2. A method according to claim 1, wherein the signal from the other detector area is provided with a weighting factor.
 3. A method according to claim 2, wherein the weighting factors are mutually opposing.
 4. A method according to claim 3, wherein the weighting factors are dependant on one another in accordance with the relationship K2=1−K1.
 5. A method according to claim 1, wherein the data signal is digitized, the digitized data signal and the data signal component contained in the wobble signal are demodulated in synchronism with one another, and the resultant signal is integrated.
 6. A method according to claim 1, wherein the data signal and the data signal component contained in the wobble signal are multiplied by one another, and the resultant signal is integrated.
 7. A method according to claim 6, wherein the data signal and/or the wobble signal is normalized.
 8. A method according to claim 6, wherein the signals from the two detector halves are normalized.
 9. A method according to claim 6, wherein the amplitude of the data signal and/or of the wobble signal is kept constant by an amplitude regulator.
 10. A method according to claim 1, wherein the data signal and/or the wobble signal is high-pass filtered before the linking data signal to the data signal component which is contained in the wobble signal.
 11. A circuit for obtaining information from a wobble track of an optical storage medium by producing a wobble signal from the difference between the signals from two photodetector areas of a photodetector, with the signal from one detector area being provided with a weighting factor, wherein the said circuit has an adder for obtaining a data signal, and a logic unit for linking the data signal and a data signal component in the wobble signal, the output signal from which logic unit is supplied to a unit for determining a weighting signal, which adjusts the weighting factor.
 12. A circuit according to claim 11, wherein the signal from the second detector area is provided with a weighting factor, which is set by a weighting signal produced by a converter.
 13. A circuit according to claim 12, wherein the weighting factors are mutually opposed.
 14. A circuit according to claim 13, wherein the weighting factors are dependent on one another in accordance with the relationship K2=1−K1.
 15. A circuit according to claim 11, wherein the said circuit has a comparator for digitizing the data signal, a synchronous demodulator for multiplication of the digitized data signal and the data signal component in the wobble signal, and an integrator for integration of the output signal from the synchronous demodulator.
 16. A circuit according to claim 11, wherein the said circuit has a multiplier which multiplies the data signal and the data signal component in the wobble signal by one another, and has an integrator which integrates the output signal from the multiplier.
 17. A circuit according to claim 16, wherein the said circuit has an averager and a normalizer for normalizing the data signal and/or the wobble signal.
 18. A circuit according to claim 16, wherein the said circuit has an amplitude regulator for keeping the amplitude of the data signal and/or of the wobble signal constant.
 19. A circuit according to claim 11, wherein the said circuit has a filter for high-pass filtering the data signal and/or the wobble signal before linking the data signal to the data signal component which is contained in the wobble signal.
 20. Appliance for reading from and/or writing to optical storage media, wherein said appliance has a circuit according to claim
 11. 